The present invention relates to a gumming device for applying adhesive to sheet material.
More specifically, the present invention relates to a gumming device for applying adhesive to cardboard blanks on a packing machine.
Gumming devices are known, which comprise a vessel containing adhesive; and a rotary, substantially roller-shaped gumming member for withdrawing part of the adhesive in which it is partly immersed, and the peripheral surface of which comprises projections with cavities for retaining and applying part of the adhesive to predetermined parts of the blanks.
Such gumming devices also comprise scraping devices for removing surplus adhesive from the peripheral surfaces of the projections outside the cavities, and which are located, with respect to the traveling direction of the blanks, upstream from where the adhesive is applied to the blanks; and a rotary, substantially cylindrical pressure member tangent to, and for pressing the blanks against, the gumming member.
Such gumming devices may also comprise a rotary, substantially cylindrical transfer member for withdrawing and transferring part of the adhesive from the vessel to the gumming member, and which is interposed between the adhesive, in which it is partly immersed, and the gumming member to which it is substantially tangent.
The scraping devices of gumming devices of the above type are fixed and so shaped as to skim the peripheral surfaces of the projections as the gumming member rotates, to remove surplus adhesive from the peripheral surfaces outside the cavities. Scraping devices of this sort, however, fail to prevent a certain amount of adhesive from accumulating, during operation, in portions of the gumming member extending between adjacent projections, on account of the distance between these portions and the scraping devices. As a result, the packing machine must be stopped frequently to clean the peripheral surface of the gumming member and prevent the gumming member from also depositing traces of adhesive on other than said predetermined parts of the blanks.
To eliminate the above drawback, a gumming device of the above type has been proposed featuring movable scraping devices controlled by cam members so as to follow the whole contour, i.e. the whole peripheral surface, of the gumming member as it rotates. Such a device, however, fails to provide for fully eliminating the drawback, owing to the difficulty encountered in maintaining substantial contact between the movable scraping devices and the contour of the gumming member at modern packing machine speeds.